package org.apache.lucene.analysis;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.File;
import java.io.IOException;
import java.io.Reader;
import java.util.Arrays;
import java.util.Set;
import java.util.List;

import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.Version;

/** Filters {@link LetterTokenizer} with {@link LowerCaseFilter} and {@link StopFilter}.
 *
 * <a name="version"/>
 * <p>You must specify the required {@link Version}
 * compatibility when creating StopAnalyzer:
 * <ul>
 *    <li> As of 3.1, StopFilter correctly handles Unicode 4.0
 *         supplementary characters in stopwords
 *   <li> As of 2.9, position increments are preserved
 * </ul>
*/

public final class StopAnalyzer extends StopwordAnalyzerBase {

    /** An unmodifiable set containing some common English words that are not usually useful
    for searching.*/
    public static final Set<?> ENGLISH_STOP_WORDS_SET;

    static {
        final List<String> stopWords = Arrays.asList("a", "an", "and", "are", "as", "at", "be", "but", "by", "for", "if", "in", "into", "is", "it", "no", "not", "of", "on", "or", "such", "that", "the", "their", "then", "there", "these", "they", "this", "to", "was", "will", "with");
        final CharArraySet stopSet = new CharArraySet(Version.LUCENE_CURRENT, stopWords.size(), false);
        stopSet.addAll(stopWords);
        ENGLISH_STOP_WORDS_SET = CharArraySet.unmodifiableSet(stopSet);
    }

    /** Builds an analyzer which removes words in
     *  {@link #ENGLISH_STOP_WORDS_SET}.
     * @param matchVersion See <a href="#version">above</a>
     */
    public StopAnalyzer(Version matchVersion) {
        this(matchVersion, ENGLISH_STOP_WORDS_SET);
    }

    /** Builds an analyzer with the stop words from the given set.
     * @param matchVersion See <a href="#version">above</a>
     * @param stopWords Set of stop words */
    public StopAnalyzer(Version matchVersion, Set<?> stopWords) {
        super(matchVersion, stopWords);
    }

    /** Builds an analyzer with the stop words from the given file.
     * @see WordlistLoader#getWordSet(Reader, Version)
     * @param matchVersion See <a href="#version">above</a>
     * @param stopwordsFile File to load stop words from */
    public StopAnalyzer(Version matchVersion, File stopwordsFile) throws IOException {
        this(matchVersion, WordlistLoader.getWordSet(IOUtils.getDecodingReader(stopwordsFile, IOUtils.CHARSET_UTF_8), matchVersion));
    }

    /** Builds an analyzer with the stop words from the given reader.
     * @see WordlistLoader#getWordSet(Reader, Version)
     * @param matchVersion See <a href="#version">above</a>
     * @param stopwords Reader to load stop words from */
    public StopAnalyzer(Version matchVersion, Reader stopwords) throws IOException {
        this(matchVersion, WordlistLoader.getWordSet(stopwords, matchVersion));
    }

    /**
     * Creates
     * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     * used to tokenize all the text in the provided {@link Reader}.
     * 
     * @return {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     *         built from a {@link LowerCaseTokenizer} filtered with
     *         {@link StopFilter}
     */
    @Override
    protected TokenStreamComponents createComponents(String fieldName, Reader reader) {
        final Tokenizer source = new LowerCaseTokenizer(matchVersion, reader);
        return new TokenStreamComponents(source, new StopFilter(matchVersion, source, stopwords));
    }
}
